␥-Secretase cleavage of ␤-amyloid precursor protein (APP) is crucial in the pathogenesis of Alzheimer disease, because it is the decisive step in the formation of the C terminus of ␤-amyloid protein (A␤). To better understand the molecular events involved in ␥-secretase cleavage of APP, in this study we report the identification of a new intracellular long A␤ species containing residues 1-46 (A␤ 46 ), which led to the identification of a novel -cleavage site between the known ␥-and ⑀-cleavage sites within the transmembrane domain of APP. Our data clearly demonstrate that the new -cleavage is a presenilin-dependent event. It is also noted that the new -cleavage site at A␤46 is the APP717 mutation site. Furthermore, we show that the new -cleavage is inhibited by ␥-secretase inhibitors known as transition state analogs but less affected by inhibitors known as non-transition state ␥-secretase inhibitors. Thus, the identification of A␤ 46 establishes a system to determine the specificity or the preference of the known ␥-secretase inhibitors by examining their effects on the formation or turnover of A␤ 46 .The amyloid deposits in the brain of Alzheimer disease (AD) 1 patients are principally composed of the 39 -43-amino acid residue amyloid ␤-peptide (A␤), which is derived from a large ␤-amyloid precursor protein (APP). In the amyloidogenic pathway, APP is first cleaved at the N terminus of A␤ sequence by ␤-secretase, to produce a soluble ectodomain, sAPP␤, and a membrane-anchored C-terminal fragment, CTF␤. CTF␤ is then subsequently cleaved within the transmembrane domain by ␥-secretase to produce the full-length A␤ and the intracellular domain (AICD) (1). ␤-Secretase has been identified as a type I membrane aspartyl protease (2, 3). The findings that knockout of presenilin 1 (PS1) and PS2 results in the abolishment of the ␥-secretase cleavage of APP and that two aspartate residues in two transmembrane domains of presenilin have been identified as critical for the ␥-secretase activity suggest that presenilin may be the ␥-secretase (4 -7). Recently, several other molecules, namely nicastrin, Aph-1, and Pen-2, have been identified as essential components of the ␥-secretase complex of which presenilin may function as the catalytic subunit (8).Most of the A␤ species contain 40 or 42 amino acids. Recently, sequence analysis revealed that the N terminus of AICD starts at residue 50 of the A␤ sequence, which is 7-9 amino acids away from the C termini of A␤ 40 and A␤ 42 . This led to the finding of the ⑀-cleavage site between A␤49 and A␤50 (9 -12). Now the cleavage at A␤40/42 has been specifically referred to as ␥-cleavage site (12). However, neither the intermediate A␤ peptide, which ends at the ⑀-cleavage site, nor the C-terminal fragment, which starts with an N terminus generated by ␥-cleavage, has ever been detected. One possibility is that ␥-and ⑀-cleavages occur simultaneously. The other possibility is that there may be additional cleavages(s) between ␥-and ⑀-cleavages. Here we report that, in our effort to determine th...

␤-Amyloid precursor protein apparently undergoes at least three major cleavages, ␥-, ⑀-, and the newly identified -cleavage, within its transmembrane domain to produce secreted ␤-amyloid protein (A␤). However, the roles of ⑀-and -cleavages in the formation of secreted A␤ and the relationship among these three cleavages, namely ⑀-, -, and ␥-cleavages, remain elusive. We investigated these issues by attempting to determine the formation and turnover of the intermediate products generated by these cleavages, in the presence or absence of known ␥-secretase inhibitors. By using a differential inhibition strategy, our data demonstrate that A␤ 46 is an intermediate precursor of secreted A␤. Our co-immunoprecipitation data also reveal that, as an intermediate, A␤ 46 is tightly associated with presenilin in intact cells. Furthermore, we identified a long A␤ species that is most likely the long sought after intermediate product, A␤ 49 , generated by ⑀-cleavage, and this A␤ 49 is further processed by -and ␥-cleavages to generate A␤ 46 and ultimately the secreted A␤ 40/42 . More interestingly, our data demonstrate that ␥-cleavage not only occurs last but also depends on -cleavage occurring prior to it, indicating that -cleavage is crucial for the formation of secreted A␤. Thus, we conclude that the C terminus of secreted A␤ is most likely generated by a series of sequential cleavages, namely first ⑀-cleavage which is then followed by -and ␥-cleavages, and that A␤ 46 produced by -cleavage is the precursor of secreted A␤ 40/42 .The mechanism of the formation of the ␤-amyloid protein (A␤) 2 is the central issue in Alzheimer disease research, not only because A␤ is the major constituent of senile plaques, one of the neuropathological hallmarks of Alzheimer disease, but also because A␤ formation may be a causative event in the disease (1). A␤ is proteolytically derived from a large single transmembrane protein, the ␤-amyloid precursor protein (APP), as a result of sequential cleavages by ␤-and ␥-secretases (1). ␤-Secretase has been identified as a type I membrane aspartyl protease (2, 3). Although the exact nature of ␥-secretase is still a matter of debate, accumulating evidence supports the idea that ␥-secretase is a multiple molecular complex composed of, at least, presenilins, nicastrin, Aph-1, and Pen-2 and that presenilin may function as the catalytic subunit (4).In understanding the mechanism by which the C termini of secreted A␤ are generated during the processing of APP, three major intramembranous cleavages have been established. The first one is the cleavage now specifically referred to as ␥-cleavage (5), which produces the C termini of most of the secreted A␤ species that end at amino acids 40 (A␤40) or 42 (A␤42) of the A␤ sequence. The second one is the ⑀-cleavage occurring between A␤ residues 49 and 50, which produces the N terminus of most of the APP intracellular domain (AICD) (5-8). The identification of this ⑀-cleavage site raises a question as to whether this ⑀-cleavage is obligatory for the generation of the...

Diversity and plasticity are the hallmarks of cells from the monocyte–macrophage lineage. Macrophages undergo classical M1 or alternative M2 activation in response to the microenvironment signals. Several transcription factors, such as peroxisome proliferator-activated receptors, signal transducers and activators of transcription, CCAAT-enhancer-binding proteins, interferon regulatory factors, Kruppel-like factors, GATA binding protein 3, nuclear transcription factor-κB, and c-MYC, were found to promote the expression of specific genes, which dictate the functional polarization of macrophages. Importantly, these transcription factors can be regulated by microRNAs (miRNAs), a group of small non-coding RNAs, which regulate gene expression through translation repression or mRNA degradation. Recent studies have also revealed that miRNAs control macrophage polarization by regulating transcription factors in response to the microenvironment signals. This review will summarize recent progress of miRNAs in the transcriptional regulation of macrophage polarization and provide the insights into the development of macrophage-centered diagnostic and therapeutic strategies.